The Gathering

In recent years, a cult has sprung up among demons which revives the ancient "religion" that hopes for the return of the demon era, spurred on by one of the signs of this alleged coming apocalypse, the appearance of the "Slayer army." They have been attacking human champions (e.g., the Slayers, Connor, etc) by making their nightmares come to life (It's An Ordinary Life). In Connor's case, he had to fight an apparently revivified Sahjhan, who came after his family. In Buffy's case, Slayers were dying, and when she finally sees who the culprit is, it seemed to be "Angelus" and "Spike"--only it was not really them.

In L.A., the demon cult recruits new members through a secret "Fight Club" (Though This Be Madness). Those demons strong enough to survive the initiation are invited into this special society. In It's An Ordinary Life, Faith and Aiden visit a demon "temple" where the Gathering perform their magicks against the champions of humanity. In Maelstrom, Illyria learns of this cult, and becomes intrigued by their goals.

To approach them, however, she must prove her true identity. She does so with the Stone of Skol, an ancient artifact that reveals a being's true essence. The Gathering rally around her as the King of Old Ones they have been waiting for. Under her leadership, they are planning to destroy the slayers and bring hell back to the Earth.

To that end, they stoke up a large energy sphere in a vast cavern below their mansion, which will soon split open and destroy all gates between hell and Earth.